I have the same problem. I swear, I think getting sleepy on rainy days is a carryover from childhood. I can remember napping during the rain, just listening to it hit the windows and roof. In Florida (where I am), this poses a big problem for me, because during the summertime it rains EVERY DAY. It is raining right now!!! I would nap, but I'm sure my younger kids (4 and 2) might burn the house down around me :)
I am beyond thankful that someone invented 5 hour energy. Nothing wakes me up faster than a maximum strength 5 hour. Nothing.